Since diabetes mellitus is a major cause of morbidity and mortality in the United States largely due to the association of coronary artery disease, we propose to test the following hypotheses regarding mechanisms of microvascular control during metabolic stress and ischemia in diabetes. Our first goal is to determine the mechanism of impaired coronary vasodilation in diabetic and acutely hyperglycemic dogs to graded reductions in perfusion pressure. To achieve this goal, three subaims will be evaluated: a) determine the segmental microvascular vasodilator reserve in diabetic and hyperglycemic dogs following coronary stenoses; b) determine the role of enhanced endoperoxide production distal to coronary stenoses in diabetes and hyperglycemia; and c) determine the role of oxygen-derived free radicals distal to a coronary stenoses in diabetes and hyperglycemia. The second major goal of these studies is to test the hypotheses that coronary vasodilation to increased metabolic demand is impaired in diabetic and acutely hyperglycemic animals. To further our understanding in this area we will evaluate the role of arginine-derived nitric oxide in ATP-sensitive potassium channels in normal, diabetic and hyperglycemic dogs. We will also evaluate the role of enhanced endoperoxide production and/or free radical generation in mediating this response. The third major goal of this experiment is to test the clinically relevant hypothesis that the class of drug therapy (insulin versus glibenclamide) will differentially affect the coronary microvascular response to ischemia in diabetic dogs. To test these hypotheses three groups of dogs will be studied: normal euglycemic dogs, alloxan-induced diabetic dogs and acutely hyperglycemic dogs. For the first two major goals euglycemic, alloxan-induced diabetic dogs (l week) and acute hyperglycemic dogs will be studied. For the third major goal, dogs with alloxan-induced diabetes of three months duration will be used. Hemodynamics, coronary perfusion pressure and myocardial perfusion will be measured during all experiments. Epicardial coronary microvascular diameters will be measured in the in vivo intact beating left ventricle preparation using jet ventilation timed to the cardiac cycle and stroboscopic epi-illumination coupled with intravital microscopy. We anticipate that these studies will identify mechanisms responsible for the increased cardiovascular morbidity and mortality in diabetic patients.